Material-selective etching of InP and an InGaAsP alloy

Wet chemical etchants are inexpensive and can be employed easily in device fabrication. Material-selective etchants extend the design flexibility for devices with heterostructures. Several etchants on (100) InP and LPE-grown (100) InGaAsP are studied with emphasis on smooth crystal surfaces and well-defined mesa-structures by use of photoresist. The best results are obtained with the system glycerine: HCl HClO₄ for preferential attack of InP and with the system H₂O H₂SO₄ H₂O₂ for preferential etching of InGaAsP. Detailed information is given on the etching solutions investigated, on the etching conditions and the etching rates of the most useful etchants.     

Many-impurity effects in a weakly interacting Kondo system: Comparison of theory with experiment

The theory of the many-impurity Kondo system developed in a previous paper is coupled with a statistical model, using a phenomenological relationship between the magnetic susceptibility and the effective Kondo temperature, to obtain the magnetic susceptibility of a very dilute Kondo system well below the single-impurity Kondo temperature. We find that the magnetic susceptibility can be represented as arising from a single-impurity effect proportional to the impurity concentration c, another term proportional to c ², as well as a much smaller c ³ contribution. The coefficient of the c ² term in has an approximate Curie law behavior at sufficiently low temperatures. The detailed temperature and concentration dependence of is in very good quantitative agreement with experiment, and is the first theoretical explanation of the anomalous magnetic susceptibility for Cu-Fe below T _K. The modification of the susceptibility arises in the theory from the inhibition of the spin-compensated state by the impurity-impurity interaction. The latter renormalizes the ln T term even in the region of temperature where the system is magnetically completely disordered.Part of this work was supported by USAFOR, under contract 73-2430 during a summer visit at Yeshiva University.     

Rate-dependent premature beats in man

Ventricular premature beats (VPBs) appeared in a patient after pacemaker insertion for complete heart block secondary to acute myocardial infarction. Contrary to expectations, the frequency of VPBs was directly related to the basic pacemaker rate. The VPBs are either reentrant beats or represent VPBs arising from pacemaker cells with "slow-response" characteristics, which have been shown to become more automatic with increasing rates of electrical stimulation. This case documents the phenomenon of rate dependency of VPBs in man and discusses its practical importance.     

Adoption and Cognitive Development: A Meta-Analytic Comparison of Adopted and Nonadopted Children's IQ and School Performance.

This meta-analysis of 62 studies (N=17,767 adopted children) examined whether the cognitive development of adopted children differed from that of (a) children who remained in institutional care or in the birth family and (b) their current (environmental) nonadopted siblings or peers. Adopted children scored higher on IQ tests than their nonadopted siblings or peers who stayed behind, and their school performance was better. Adopted children did not differ from their nonadopted environmental peers or siblings in IQ, but their school performance and language abilities lagged behind, and more adopted children developed learning problems. Taken together, the meta-analyses document the positive impact of adoption on the children's cognitive development and their remarkably normal cognitive competence but delayed school performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Science and technology in the region: The output of regional science and technology, its strengths and its leading institutions

Summary We operationalize scientific output in a region by means of the number of articles (as in the SciSearch database) per year and technology output by means of the number of patent applications (as in the database of the European Patent Office) per priority year. All informetric analyses were done using the DIALOG online-system. The main research questions are the following: Which scientific and technological fields or topics are most influent within a region and which institutions or companies are mainly publishing articles or holding patents? Do the distributions of regional science and technology fields and of publishing institutions follow the well-known informetric function? Are there - as it is expected - only few fields and few institutions which dominate the region? Is there a connection between the economic power of a region and the regional publication and patent output? Examples studied in detail are seven German regions: Aachen, Düsseldorf, Hamburg, Köln (Cologne), Leipzig - Halle - Dessau, München (Munich), and Stuttgart. Three different indicators were used, science and technology attraction of a region (number of scientific articles and patents), science and technology intensity (articles and patents per 1,000 inhabitants), and science and technology density (articles and patents per 1 billion EURO gross value added). Top region concerning both attraction and intensity is Munich, concerning density it is Aachen.     

Deoxidisation and phase analysis of plasma sprayed TiO2 by X-ray Rietveld method

It is fundamentally important to determine the deoxidisation and phase compositions of plasma sprayed TiO₂ coatings containing anatase. In the present study, plasma sprayed porous TiO₂ coatings containing anatase were prepared using anatase powder and both Ar-He-H₂ and Ar-He-N₂ plasma gases. The deoxidisation of TiO₂ and phase compositions of the starting powder and the prepared coatings were examined using X-ray Rietveld method by refining their crystalline parameters and scale factors. The refined oxygen occupancies showed that there were about 0.08 and 0.1 formula units of oxygen deficiencies for the rutile and anatase phases of the coatings, respectively. Such degrees of deoxidisation and the other crystalline parameters appeared independent of the plasma spraying process parameters. With considerations of the presence of organic adhesive in the starting powder and the formation of titanium ethoxide in the coatings, the degrees of deoxidisation estimated by the X-ray Rietveld method were slightly higher than those quantified by the thermogravimetry curves. The phases of the coatings determined from the refined scale factors were mainly composed of rutile with 10.0% to 22.5% anatase by weight, and the latter content increased with decreasing the intensity of the plasma jet.     

“The big sweep”: On the power of the wavefront approach to Voronoi diagrams

We show that the wavefront approach to Voronoi diagrams (a deterministic line-sweep algorithm that does not use geometric transform) can be generalized to distance measures more general than the Euclidean metric. In fact, we provide the first worst-case optimal (O (n logn) time,O(n) space) algorithm that is valid for the full class of what has been callednice metrics in the plane. This also solves the previously open problem of providing anO (nlogn)-time plane-sweep algorithm for arbitraryL _k -metrics. Nice metrics include all convex distance functions but also distance measures like the Moscow metric, and composed metrics. The algorithm is conceptually simple, but it copes with all possible deformations of the diagram. Research partially supported by the Natural Sciences and Engineering Research Council of Canada. Research partially supported by the Deutsche Forschungsgemeinschaft, Grant No. Kl 655/2-1.     

Rendering of multiresolution models with texture

State of the art multiresolution modeling allows to selectively refine a coarse mesh of an object on the visually important parts. In this way it is possible to render the geometry of a given object accurately with a minimum number of triangles. The criteria used in current approaches take care of geometric error and even of shading errors. If however texture mapping is used it is inevitable to control displacements and distortions of the texture during refinements.     

Photoresist application for the LIGA process

 Fabrication of high aspect ratio structures requires the use of a photoresist able to form a mold with vertical sidewalls. Thus the photoresist should have a high selectivity between the exposed and the unexposed area in the developer. It should be relatively free from stress when applied in thick layers necessary to make high aspect ratio structures. PMMA (Poly Methyl Methacrylate) is the photoresist of choice in the LIGA process, mainly for its ability to hold vertical sidewalls for tall structures. It is applied to the substrate by a glue-down process in which a pre-cast, high molecular weight, sheet of PMMA is attached to the plating base on a substrate. The applied photoresist is then milled down to the precise height by a fly-cutter prior to pattern transfer by x-ray exposure. The requirement that the applied layer be relatively free from stress dictates the choice of glue-down over casting. The substrate preparation steps, as well as the conditioning of the PMMA sheet prior to the glue-down, are done, in part, to reduce the stress in the glued down sheet of photoresist. The cutting of the PMMA sheet in the fly-cutter requires specific operating conditions as well as particular cutting tools to avoid introducing any stress and the resultant crazing of the photoresist. Received: 25 August 1997/Accepted: 3 September 1997